It is known that the illumination quality and the property of the light of a lighting device are related to the way that light beams generated by the lighting device are being transmitted. Lighting analysis of a lighting device incorporates lighting levels and lighting quality considerations such as glare, uniformity of illuminance, and color rendition into a lighting survey. Generally, a lighting device uses reflecting screens and shielding screens to control the directions of the light emitted therefrom and thus enable the luminous intensity of the same to be distributed uniformly. Conventionally, lighting devices usually adopt semi-transparent plastic screen or louver as shielding screen for reducing glare. However, since the semi-transparent plastic screen is inferior in that it is capable of not only absorbing light, but also diffusing light, the lighting device adopting semi-transparent plastic screen as shielding screen will have poor energy efficiency and glare control. In addition, the light source of a conventional lighting device must be positioned precisely at a specific location so as to enabling the luminous intensity of the lighting device to be distributed as desired.
Please refer to FIG. 1, which is a light box having a Fresnel lens 1 disclosed in U.S. Pat. No. 4,704,004. The light box 10 of FIG. 1 uses a parabolic reflector 14 for enabling light beams to be discharged therefrom parallelly. The light source 12 arranged in the light box 10 comprises a line source such as a fluorescent tube, which can be adopted as the light source of a liquid crystal panel. However, since the goal of the light box 10 is to discharge parallel rays, the types and structures of the light source are thus limited.
In addition, an illumination fixture, disclosed in U.S. Pat. No. 6,206,544, uses the cooperative operation of a cold cathode tube and a catadioptric lens to collect and redirect light beams toward a Fresnel lens arranged at the light emitting end of the illumination fixture for directing and spreading the emitted light to fill an illumination field. Although the direction and distribution of the emitted light is controllable by the catadioptric lens, it is bulky and complicated that is not cost effective.
Therefore, it is in great need to have a lighting device with integration sheet capable of overcoming the aforesaid shortcomings.